Axial blower apparatus, such as propeller fans and the like, generally find application as air blower apparatus for use in air conditioning apparatus outdoor units. Referring to FIGS. 16–18, there is shown a structure of an air conditioning apparatus outdoor unit which employs such an air blower apparatus.
As shown in each of the figures, the aforementioned air conditioning apparatus outdoor unit comprises a main body casing (1) in which an air blower apparatus unit (3) is disposed on the air flow downstream side of a heat exchanger (2) on the side of a rear air inlet (10a). This air blower apparatus unit (3) is made up of a propeller fan (4) which is an axial blower apparatus, a bell-mouth (5), situated on the side of an outer periphery of the propeller fan (4), by which a suction region (X) on the rear side of the propeller fan (4) and a discharge region (Y) on the front side of the propeller fan (4) are partitioned from each other, and a fan guard (6) situated on the discharge side of the propeller fan (4) (i.e., on the front side of the propeller fan (4)).
The rear air inlet (10a) is formed in a rear surface of the main body casing (1), and a side air inlet (10b) is formed in a side surface of the main body casing (10). Additionally, the interior space of the main body casing (10) is divided, by a partition plate (7), into two chambers, namely a heat exchange chamber (8) and a machine chamber (9). Disposed in the heat exchange chamber (8) are a heat exchanger (2) which is L-shaped in transverse section and located face to face with both the rear air inlet (10a) and the side air inlet (10b) and the aforesaid air blower apparatus unit (3) which is located downstream of the heat exchanger (2). On the other hand, disposed in the machine chamber (9) are a compressor (11) and other component parts. A fan motor (12) for rotatably driving the propeller fan (4) is supported fixedly on a fan motor holding bracket (not shown diagrammatically) disposed downstream of the heat exchanger (2).
The propeller fan (4) is, for example as shown in FIG. 19, linkup-fixed to a drive shaft (12a) of the fan motor (12), and comprises a hub (14) which becomes a center of rotation of the propeller fan (4) and a plurality of identical blades (13, 13, 13) which are disposed integrally along an outer peripheral surface of the hub (14). The blade (13, 13, 13) is formed into a swept-forward blade superior in air supplying performance, wherein, at leading and trailing edges (13a) and (13b) of the blade (13, 13, 13), the position of an outer peripheral end (R) of each edge is situated ahead, relative to the direction of rotation F of the propeller fan (4), of the position of a hub side base end (S) (i.e., the inner peripheral end).
Such an outdoor unit construction may produce inconvenience, i.e., high levels of noise during operation because of the noise generated by the propeller fan (4) itself and, in addition, because of the noise generated upon collision of an air flow discharged from the propeller fan (4) against a downstream structural member such as a fan guard (6) et cetera.
With a view to reducing the total noise of an air blower apparatus (e.g., a propeller fan) of the above-described type that is employed as an air blower apparatus for use in air conditioning apparatus outdoor units, various measures and examinations, such as the optimization of the blade-surface shape of propeller fan blade sections and the thickening of blades for superior aero-performance, have so far been made. Unfortunately, these noise-reduction methods alone fail to provide solutions to the following problems.
When the blades (13, 13, 13) of the propeller fan (4) having a blade structure of FIG. 20 start rotating, this produces an air flow (α) on the side of an outer peripheral part (13c) of a blade (13). This air flow (α) enters from the side of a pressure surface (13d) of high pressure around into the side of a suction surface (13e) of low pressure. The air flow (α) forms a blade tip vortex (β) as shown in the figure. Discharge air flow turbulence caused by the blade tip vortex (β) becomes laminated as the air flow moves downstream, and gradually grows and increases (see FIGS. 21 and 22). The discharge air flow finally moves away from the suction surface (13e) of the blade (13), and interferes with the pressure surfaces (13d, 13d) of the adjoining blades (13, 13), with an inner peripheral surface of the bell-mouth (5), and with a structural member disposed downstream of the air blower apparatus such as the fan guard (6) et cetera, thereby increasing the noise to higher levels. Particularly, as shown in FIG. 22, a blade tip vortex (β) at a distance from the suction surface (13e) of the blade (13) will undergo greater turbulence when interfering with the adjoining blades (13, 13). As a result, the blade tip vortex (β) is discharged downstream of the air blower apparatus. This increases levels of noise to a further extent.
Such a phenomenon appears significantly, particularly when reducing the chord length of the blade (13, 13, 13) to achieve weight and cost saving of the air blower apparatus, because such reduction reduces the blade cascade effect of the blade (13, 13, 13). More specifically, as shown in FIG. 23, the blade tip vortex (β) tends to leave the suction surface (13e) and interferes early with the adjoining blades (13, 13) in comparison with the aforesaid case.
To cope with the above, the inventors of the present invention previously disclosed, as a technique for suppressing blade tip vortexes as discussed above to reduce levels of noise generated by air blower apparatus such as propeller fans, an improved air blower apparatus (Japanese Patent Application No. 2001-388966). As shown in FIGS. 24–26, an outer peripheral part (13c) of the blade (13, 13, 13) of the air blower apparatus is provided with a camber part which becomes gradually greater in radial-direction width from the vicinity of a leading edge toward the vicinity of a trailing edge thereof Such arrangement ensures that blade tip vortexes are suppressed without changing the entire shape of the blade (13, 13, 13).
In other words, the above-described air blower apparatus of the previous invention (which is made up of a hub (14) which becomes a center of rotation as shown in the figure and a plurality of blades (13, 13, 13) disposed along an outer peripheral surface of the hub (14) wherein the blade (13, 13, 13) has a leading edge (13a) and a trailing edge (13b), and outer peripheral ends of these edges are situated ahead relative to the direction of rotation) is characterized in that the blade (13, 13, 13) is formed such that its outer peripheral part (13c) is recurved toward the suction side and such a camber part of the outer peripheral part (13c) becomes gradually greater in radial-direction width from the vicinity of the leading edge (13a) toward the vicinity of the trailing edge (13b).
As described above, in the blade (13, 13, 13) of the air blower apparatus (such as a propeller fan et cetera) which is a so-called swept-forward blade in which the outer peripheral end is situated ahead, relative to the direction of rotation, of the inner peripheral end at the leading and trailing edges (13a) and (13b) of the blade (13, 13, 13), the outer peripheral part (13c) is recurved toward the suction side. As a result of such arrangement, on the side of the outer peripheral end (R) of the blade (13, 13, 13), an air flow is allowed to smoothly flow around and enter into the concave circular arc-shaped, suction surface (13e) along the convex circular arc-shaped, pressure surface (13d), as shown in FIG. 24. Therefore, the diameter of the blade tip vortex (β) becomes smaller and stable, and an air flow flowing in the direction of the blade outer periphery on the side of the suction surface (13e) will no longer interfere with the blade tip vortex (β).
If the width, W, of the camber part of the blade outer peripheral part (13c) gradually increases from the vicinity of the leading edge (13a) to the vicinity of the trailing edge (13b) as described above, the above-described action achieves its effect smoothly from the leading edge's (13a) side to the trailing edge's (13b) side according to the diameter of the blade tip vortex (β) whose diameter increases when gradually laminated to become larger from the leading edge's (13a) side to the trailing edge's (13b) side of the blade (13, 13, 13) (see FIG. 25). In addition, the generated blade tip vortex (β) is unlikely to depart from the blade suction surface (13e).
Consequently, even when the chord length of the blade (13, 13, 13) is shortened for the purpose of weight saving as shown in FIG. 26, blade tip vortexes (β) will not interfere mutually between the adjoining blades (13, 13, 13), and they are discharged downstream of the air blower apparatus. As a result, the level of noise generated from the air blower apparatus itself is effectively reduced.
Problems to be Solved
It is true that the above-mentioned previous application provides an improved construction capable of achieving blade tip vortex reduction, and of preventing blade tip vortex interference between adjoining blades.
However, for the case of the previous application construction, it has become clear that there is still room for improvement with respect to the point that a generated blade tip vortex grows, and is discharged downstream of the air blower apparatus.
Since such an air blower apparatus is generally employed as an air blower apparatus for use in air conditioning apparatus outdoor units as described above, it is natural that there is a grilled structural member such as a fan guard at a position immediately downstream of the air blower apparatus. Accordingly, when incorporated within the air conditioning apparatus outdoor unit, discharge vortexes from between adjoining blades will interfere with the grilled structural member, thereby generating noise.
In order to provide solutions to these problems, the present invention was made. Accordingly, an object of the present invention is to provide an air blower apparatus capable of achieving blade tip vortex reduction without making any change in the entire blade shape, capable of suppressing the discharging of vortexes to the air blower apparatus downstream side without fail, and capable of effective reduction in noise levels even when incorporated within an air conditioning apparatus outdoor unit, by employing such an arrangement that a blade outer peripheral part of the air blower apparatus is provided with a bent part which becomes gradually greater in radial-direction width from the vicinity of a leading edge toward the vicinity of a trailing edge so that it becomes a starting point at which an air flow from the side of a pressure surface to the side of a suction surface starts leaking.